Mechanical Engineering: Internal Forces on Beams (4 of 27) Direction Convention of Shears & Moments

[@jpdemont]

Thank you Professor. You are an excellent teacher.

[@mourtadaal-haiyk4364]

thank you very much. your list "Internal Forces on Beams" is very helpful and clear.

[@NisseOhlsen]

Thanks for the good videos! Suggestion for an alternative explanation that does not refer to conventions: The fact that you get a positive number for M2, indicates that you chose the correct orientation on your drawing. Had you gotten a negative number, this would be an indication that you should have drawn M2 counterclockwise.

[@LindelaniMasoko]

GREATEST OF ALL TIME

[@MichelvanBiezen]

Thank you. Glad you found our videos. 🙂

[@saidhashimmi8285]

Thank you sir you are the best professor. from Afghanistan

[@MichelvanBiezen]

Welcome to the channel!

[@12frank41]

you are the best in the whole world may god bless you

[@elextwo2190]

Mr. Biezen, you sir are a living legend!!! Thank you !! :)

[@Attalla-t9b]

Thanks, this completely clear my confusion. Turns out the relation between sign conventions and the way we do calculations in this context isn't like what we would normally thought of them 😅

[@MichelvanBiezen]

Yes indeed. There is a convention of how to think about them.

[@umitdev7045]

nice. i think that one most important topic in statics

[@XplosiveAction]

When you say "by convention" like with the V and M vectors, are you saying that nothing is really implying that they are positive or negative, and that we always start these problems by making them positive? To me it always feels like a random and forces implication. I suppose you always START with V and M in the positive convention and see if thats really the case when you do the Sum of the forces and Sum of the moments about the cut.

[@SuperGamerYoBros]

Mr.Biezen you said the wrong assumptions while doing your second beam 2. The convention on beam 2 is that CW is positive meaning (300N*2m) - (200N*4)+M2. I know you get the same answer, but what you said was different.

[@glorisamarcagaanan4442]

he explains in 8:24, why it's CW is negative.

[@elinebjrnevik5693]

Thank you for making this video :D

[@دروسالرياضياتالأساسيةللكلمنالص]

Hi, first thing I appreciate your precious time PROF MICHLE then ,,,, Mr michle I have an question about this video (why did you calculate the shear force and bending moment at two meters from point A ,where there no effect at that point ) I think you should take the cross section at the point four meters from point A (where F=300 N) , I dont know if he wanna find the S.F and B.M at that point you determine at the question . and Iam very thankful for your time to read this message .

[@paisleyt6706]

I think he just wanted to find the shear at that point. We could calculate the shear and the moment at any point along the beam and they would not all be the same.

[@pritamsingh2971]

You are brilliant sir

[@ianbeach277]

Question: When determining the internal forces at a section, what if I assumed the sign convention for a negative moment (yielding a hogging shape of the beam)? Would the result be that I determine negative moment and shear values at that section which indicates I assumed incorrectly the deflected shape of the beam? Therefore, I could then correct my assumption and know that the beam is in fact sagging and the beam is experiencing positive moment internally? Thanks!

[@MichelvanBiezen]

As long as you remain consistent throughout the problem, you can use any convention, including your own. But it is also good to learn the standard convention, otherwise it can get confusing.

[@ianbeach277]

@@MichelvanBiezen Awesome, thank you for the response!

[@anesmerazi603]

sir what causes the moments m1 and m2 ?

[@MichelvanBiezen]

The moments are the beam's response to a load place on the beam. (Note they are internal to the beam).

[@anesmerazi603]

thank you sir

[@gayathriguna3158]

This might be a silly question, but when you drew the 2 separate sections in the bottom, how did you know to draw shear to be positive and moment to be positive? Like even before you started the calculation of shear and moment?

[@MichelvanBiezen]

That is by "convention". It appears odd at first, but that is by convention.

[@TheHonchoofAllSpearheads]

sir, just wondering -- did you apply mechanical engineering in reaching up to the board in order to write that lengthy title?

[@MichelvanBiezen]

haha

[@TheHonchoofAllSpearheads]

isn't V2's value be cumulative of V1's? because that's what I learned in class. like when u split the structure into several sections, u need to consider the shear force, V from the previous adjacent section as well, @michel. can u help to clear me up?

[@craig7878]

You can do it the way you suggest that it is cumulative. But we start at the very left of beam, not even at the cut, lets say point A. The left of point A which is even left of support is V_AL = 0 since its a free end. Then V_AR (right side of support) is V_AR = V_AL + RA (RA is support reaction). Then, when we come to the point of interest where the cut is, we have V_BL (lets call point of interest B), we have V_BL = V_AR. If you do it this way you will get 100N for V1 and V2 like he did, since V_AR has accumulated the reaction force, since we used reaction to calculate it.

[@ajcrno]

why is clockwise negative? and counter clockwise positive?

[@MichelvanBiezen]

That is by convention.

[@ajcrno]

@@MichelvanBiezen hi sir is there a way i can message u privately? I kinda have some questions to ask :)

[@Minerva578]

hmmm i ask myself the same question.....

[@tnksmulatmsehu3090]

tnks

[@Easy_Uni_Math]

Great job

[@tsp8855]

wait so if m1=m2 in magnitude and v1=v2 also in magnitude, don't we just need to figure out m1 and v1 and then from there we can just say that m1=m2 and v1=v2 but in opposite directions?

[@MdFahim-oc6ke]

i am not clear about why you took v as a minus.the explanation is not clear.i am finding it hard to understand.

[@MichelvanBiezen]

V1 is the force caused by beam section 2 pushing down on beam section 1

[@MdFahim-oc6ke]

but the force is downwards.........then why it is called a positive shear force?i mean why there is difference in the conventions of shear force and force balance?

[@stephenflynn8586]

@@MdFahim-oc6ke the positive result of V1 (+100) confirms the lectures assumption of up = positive and down = negative (for this section) is true. If he assumed V1 to be in the opposite direction (up) the result would be negative and you would know that V1 is downward. As stated above section 2 pushes down on section 1 so you can safely assume V1 is downward shear the calculation confirms this. Play around with different assumption and see....someone please correct me if i am wrong.

[@MRBMN-zp4cd]

Sign convention is so confusing to me

[@MichelvanBiezen]

This is definitely a brain twister. Best to remember the rule and go with it. 🙂

[@kupkumral2793]

Kral

[@calebanderson5309]

And I'm confused about V again

[@pritamsingh2971]

What's happen

[@12frank41]

you are the best in the whole world may god bless you

[@12frank41]

you are the best in the whole world may god bless you

[@MichelvanBiezen]

Thank you